If you're a manager, you might want to enter leads into the CRM yourself and then assign them to your employees. There are two different simple ways to do this:
Assign an individual contact to a different user
When viewing a contact's profile, you'll see a box near the middle of the screen that says "Contact Info" (or "Company Info if you're looking at a company). Assuming you have the ability to see other user's contacts (which you should if you're a manager) the first item in that box will say "Assigned to ____." When you click the name of the user that the contact is currently assigned to, a box will pop up with the option to assign the contact to a different user.
Assign contacts in bulk to a different user
If you want to assign many contacts at once, you can do so from the Find a Contact page. You can filter the contacts using a search or Groups if you want to, and then just check the box next to a contact's name to indicate that you want to re-assign them. If you want to re-assign all the contacts shown, click the "Select all" link near the top left of the page. After checking the contacts, you'll see an option at the top of the screen that says "Assign to a user."